A biocular is an optical system that produces an image that a user can view with both eyes. Biocular systems have been used as a means to magnify an electronically generated image, such as an image produced by a cathode ray tube (CRT). An example biocular is described in U.S. Pat. No. 5,151,823 to Chen, issued Sep. 29, 1992 (hereafter “Chen”), the entirety of which is incorporated herein by reference as if fully set forth herein. Bioculars have been used in head-up and head-down displays in modern military vehicles such as tanks and other armored vehicles, military and commercial aircraft, flight simulators, microscopes used to inspect semiconductor devices, and medical applications. Various video sources may be used to generate images that are displayed by a biocular, such as thermal imaging systems, day sight video cameras, night vision systems, and computer generated graphics, among others. An advantage of using a biocular eyepiece in a display system, as compared to a monocular eyepiece or a binocular eyepiece, is that the observer is able to freely move her or his head and use both eyes to see essentially the same image at the same light level on the same optical system. However, unconstrained movement between the user and the display can become a problem in tactical applications, where an image may need to be viewed carefully while the user is moving, for instance during combat.
Displays that use a biocular can offer the additional advantage of presenting a large virtual image to both eyes of the viewer from a small real image source, such as a very small cathode ray tube (“CRT”). Use of a very small CRT allows the overall package of the system to be compact in size, which is an important attribute in tactical applications such as aircraft, military vehicles and the like, where space is limited.
Tactical image display systems typically use a small monochromatic CRT as the active display element. However, small monochrome CRT's are unable to display color images and are generally limited in resolution and the ability to display high definition video imagery. These deficiencies severely limit the ability of such systems to support applications that require presentation of high quality color imagery. Accordingly, a need exists for an improved image display system, including one that is compact, efficient, reliable, and adapted to produce high-quality and high-resolution color images, and particularly one that is compatible with high definition color video sources, including digital sources. A need also exists for an improved image display system that is specially adapted to be used in tactical applications, where an image may need to be viewed carefully while the user is moving, for instance during combat.